Voltage sags due to induction motor starting:
1. Voltage sags can causes:
ü Motor load to start/ stop
ü Digital devices to reset causing loss of data
ü Equipment damage and /or failure
ü Materials spoilage
ü Lost production due to downtime
ü Additional costs
ü Product reworks
ü Product quality impacts
ü Cost of investigations into problem
ü Impacts on customer relations such as late delivery.
ü Lost of sales
2. Voltage sags due to Motor Starting:
ü Voltage sag produced by induction motor starting current is one of the main causes of sensitive equipment dropout.
ü The use of motor starter reduces the voltage sag depth but increases its duration.
ü The subsequent connection to full voltage originates new sag separated from the first one by a few seconds.
ü An induction motor will draw six to ten times its full load current while starting.
ü This lagging current then causes a voltage drop across the impedance of the system.
ü Generally induction motors are balanced 3 phase loads, voltage sags due to their starting are symmetrical.
ü Each phase draws approximately the same in rush current. The magnitude of voltage sag depends on,
ü Characteristics of the induction motor
ü Strength of the system at the point where motor is connected.